The present invention relates to a pickup device detachably mountable on a stringed musical instrument having a sound body or resonance body capable of producing natural acoustic sounds, and more particularly to a pickup device for acoustic guitars having strings of magnetic material.
FIG. 1 of the accompanying drawings illustrates a stringed musical instrument having a hollow sound or resonance body, such as an acoustic guitar. To increase or strengthen sounds generated by such an acoustic guitar, it is frequently practiced to mount a pickup device in a sound hole 3 defined in a sound board 2 of the sound body 1, the pickup device being capable of converting vibrations of strings 4 into electric signals. It is such a pickup device readily removably attached to an acoustic stringed musical instrument that the present invention is concerned with.
One pickup device of the type described which has found practical use is shown in FIGS. 2 and 3. The pickup device is composed of a pickup mount 5 placed in a sound hole 3 in a sound board 2 and an electromagnetic pickup 6 supported on the pickup mount 5. The pickup mount 5 has support legs 7 fitted on peripheral edges of the sound hole 3, the support legs 7 being easily attachable to or detachable from the sound board 2. The electromagnetic pickup 6 is desinged so that it will be positioned directly below strings 4 when the pickup mount 5 is placed in the sound hole 3, as shonw in FIG. 3.
As is well known, the electromagnetic pickup 6 is capable of producing output electric signals in response to vibrations of the strings 4 which are made of magnetic material. The electric signals picked up are equivalent to electromotive forces developed in coils when a magnetic field generated by a magnet is fluctuated by the string vibrations. The output from the electromagnetic pickup 6 is fed over an output cord 8 to an output plug 9. The term "magnetic material" used herein means a material having a property capable of affecting a magnetic field in which the material is placed.
The electromagnetic of the foregoing type is of a low impedance and has an advantage in that it is immune to external noise. However, it has an actual response frequency band below the range of from 1 through 5 kHz, and is subjected to a poor response to the frequencies higher than the range. Where the pickup device is attached to a stringed musical instrument such as an acoustic guitar in which delicate sounds of high frequencies are of importance, sounds of the guitar as picked up by the pickup device are tend to be confined or "boxy" and less sharp, a sound quality which is far from the original sounds of the acoustic guitar and hence is quite unattractive.
To cope with this problem, there has been made an attmept to improve the high-frequency response by changing the thickness of the coil wire in the pickup and also changing the covering material itself for the coil and the thickness thereof to therby vary the capacitance between coil turns. However, the improvement achieved through these efforts has been quite unsatisfactory, and has failed to provide the sound quality of acoustic guitars sufficiently.